The blood and plasma activity concentrations require interpolation procedures for kinetic modeling, as described above.

Operational Model Curve

The **Gamma Function** model is defined by the following functional form:

describing a sharp peak governed followed by a quick decay towards zero.

Parameter Fitting

The **Gamma Function** model includes a **Begin **time parameter for positioning the peak. The factor **A** scales the curve, the exponent **B** governs the rise and constant **C** the decay towards zero. Use the **Fit plasma activity** or **Fit whole blood** button to fit the operational model curve to the measurements. Note that all samples are considered, not only the ones after **Begin**.

The form of the curve reacts very sensitively to changes of the parameters. The example above illustrates the inability to fit model a peak followed by a moderate to slow decay appropriately. This model may therefore be more suited for simulations rather than actual data processing.

The **Delay** parameter serves for correcting a timing offset between tissue and blood data. Positive delays correspond to delayed blood information and hence shift the blood curve to earlier times (to the left). The **Delay** is only relevant during the fitting of the tissue* *model where it can be fitted as an additional parameter to the parameters of the kinetic model.